By Jeff Peterson, editor-in-chief, Plastics Decorating

With printing technical advancements in recent years, the evolution of ink formulations, eco-friendly solutions and efficiency improvements make printing on rigid and foam-based packaging easier and more economical than ever before.

Alex Folloso, vice president of R&D Metal Decorating Technology for INX International, said there are several critical elements to consider. The first step is crucial for selecting the appropriate ink for dry offset plastic container applications. “When one chooses an ink, there are several critical questions to consider. The first is, what type of plastic material is being used?” said Folloso.

Bart Schild, business development manager for AAE North America, agreed. “One of the first things to examine is the type of plastic used,” commented Schild. “Manufacturers sometimes add additives, such as silicone, to the plastic to improve the molding process; however, the additives can negatively impact print quality.”

Four common examples include: Polypropylene (PP), a thermoplastic used in a wide variety of applications; Polyethylene (PE), a low-cost, versatile and durable plastic known for its low density, moisture and chemical resistance; Polyteraphthalate (PET), a form of polyester widely used for bottle production around the world; and Polystyrene (PS), available as either foam or rigid plastic, offering different physical properties depending on its application.

“Since different plastics have varying surface properties, they require specific ink chemistries for optimal adhesion. These variations influence aspects of the application, particularly adhesion and bonding strength,” Folloso explained.

When considering a container’s final usage conditions, it is important to account for factors such as chemical exposure, abrasion resistance and temperature fluctuations, as these will influence an ink’s durability. If regulatory and sustainability considerations come into play, compliance with food safety and environmental regulations may dictate specific ink formulations. Sustainability goals, such as recyclability requirements, also can influence which ink is chosen.

“The choice of curing technology plays a major role in ink selection, so it’s important to consider the available drying methods, whether it is UV, UV LED or conventional systems,” said Folloso. “For example, polypropylene containers often require surface pre-treatment – such as flame or corona treatment – to improve surface energy and ensure inks properly adhere. Without these treatments and the right ink formulation, achieving strong adhesion and durability can be difficult.”

“To improve ink adhesion, the surface typically is pre-treated for dry offset applications,” added Schild. “This can improve the surface tension (dyne level) and help remove or burn off part of the silicone layer, further improving print quality.”

ADVANTAGES OF UV AND UV LED INKS FOR DRY OFFSET
Folloso indicated that UV inks offer multiple benefits for dry offset printing on plastic containers, including improved adhesion and faster curing. This makes it an attractive option as dry offset printed packaging typically has better recyclability compared to shrink sleeves or in-mold labels. It also can reduce material and production costs since no separate labels are required.

“With the UV process, the ink instantly cures on the surface with minimum absorption, making it ideal for high-speed printing lines and allowing immediate post-production handling,” he explained. “These inks offer superior adhesion and durability with excellent resistance to scratches, abrasion and chemicals. Most noticeably, they deliver vibrant colors and sharp graphics that enhance print quality and brand visibility.”

“When using UV LED inks to transition a container printing line to UV LED,” Folloso said, “one can gain additional operational advantages. These include significant energy savings and faster throughput without compromising print quality.”

“LED curing lamps require significantly less energy compared to traditional UV lamps, so consumers not only reduce energy consumption but also benefit from longer lamp life. They last substantially longer, saving money and reducing downtime and maintenance costs,” he continued. “With minimal heat generation, they protect heat-sensitive plastics from warping or distortion. With no mercury content and lower VOC emissions, they also reduce environmental impact.”

Schild agreed that using UV inks for dry offset provides several advantages, allowing for immediate handling and further processing with shorter curing times. “The process is clean, generating less waste and requiring minimal cleanup,” added Schild. He pointed out that UV or UV LED inks also provide the ability to apply multiple colors in a single stroke, significantly reducing the time and steps needed in multi-color printing.

TROUBLESHOOTING INK COVERAGE ISSUES
Working with rigid and foam-based packaging requires an understanding of the ink properties, surface conditions and process parameters. Ultimately, it comes down to three key factors: ink adhesion, drying time and managing print defects, like dot gain and ghosting. Achieving optimal results often involves fine-tuning the ink formulation, enhancing surface treatment of the plastic substrate and adjusting press settings.

Schild stated that ink formulation certainly is a key factor in achieving proper ink coverage and troubleshooting dry offset container applications. “Components can be added to the ink to improve how well the ink bonds to the surface,” he explained. Utilizing the correct ink can help dry offset printed containers run at optimum speeds and achieve reliable print quality throughout extended production runs.

Folloso said when it comes to troubleshooting ink coverage issues, it’s important to look at the whole process. “Incorrect viscosity is a common culprit behind uneven coverage or ink transfer issues. The good news is that it’s easily corrected by adjusting viscosity with the right solvents or additives,” he explained.

“Surface treatment quality is another critical factor. If corona or flame treatment isn’t sufficient, adhesion will suffer. For example, if poor ink coverage on a PE container is seen, increasing the corona treatment intensity and confirming proper ink viscosity often resolves the issue,” continued Folloso.

“Press maintenance also plays a role,” he said. “Worn or improperly cleaned plates and blankets can cause uneven ink transfer, so regular cleaning is essential. Ensuring the ink formulation matches the plastic type also is crucial. Using the wrong formulation often results in poor coverage or adhesion.”

CONTAINER SIZE IMPACT ON INK CHOICE
“Larger or irregularly shaped containers might require inks with extended open time frames or enhanced transfer properties to maintain consistency and prevent premature drying on the press. Smaller containers, on the other hand, may benefit from higher pigment concentration or faster curing capabilities to achieve sharp, clear images,” Folloso noted.

It is important to remember that container size affects curing methods and equipment set-up, which in turn impacts the practical selection of UV and UV LED inks. For example, smaller cosmetic containers often use highly pigmented, fast-curing UV LED inks to produce detailed, vibrant graphics at high production speeds. These vivid designs help the product stand out on store shelves and attract consumers’ attention.

“Larger containers may require inks formulated with extended open times or enhanced transfer properties to prevent drying or transfer issues during longer print runs. If the inks dry too quickly on press, it can lead to poor transfer, incomplete coverage or defects on the final product. This ensures consistent coverage across the entire surface without defects,” explained Folloso.

CONCLUSION
Dry offset printing offers key advantages over other secondary decorating processes – most notably is the high production speed it allows, making it ideal for large-scale manufacturing. “Keeping important factors in mind, including plastic composition, surface treatment selection, ink formulation and the correct curing process and intensity, are key to success,” stated Schild.

Folloso pointed out that selecting the right ink formulation for rigid and foam-based packaging is critical to maintaining both print quality and production efficiency. It goes far beyond choosing a standard formulation and requires a thorough understanding of the substrate, printing process and performance requirements.

“By evaluating factors such as plastic type, curing technology, container size and operational goals, printers can overcome common challenges and produce packaging that meets both production demands and brand expectations. With ongoing advancements in UV and UV LED technologies, the industry is well-positioned to achieve greater efficiency, sustainability and eye-catching designs that drive consumer impact,” concluded Folloso.

INX International is the third-largest producer of inks and coatings in North America, with full-service subsidiaries in Europe and South America, and is part of Sakata INX worldwide operations. For more information, visit www.inxinternational.com.

AAE provides high-tech printing and assembly solutions for plastics decorating applications, including inkjet, dry offset and pad printing, as well as pre- or post-treatments. For more details, visit www.aae.tech/na.